This invention relates to a lead-free continuously-cast copper-base alloy suited for use as a bearing, bushing, or guide material.
Currently there are different specifications covering many bearing bronzes, the most popular of them being those of Copper Development Association (CDA). Some of these bearing bronzes are lead-free, for example, C903 or C954. Others are leaded, for example, C932 and C936. Lead-free bronzes like C903 and C954 have high coefficient of friction in metal to metal rubbing contact and also have lower machinability compared to leaded bronzes.
Leaded bronzes have good machinability and have low coefficient of friction. However, they contain anywhere from 5 to over 15 percent lead in them. During the past two decades it has been established that ingestion of even a few parts per billion of lead into human body causes severe health problem. As a consequence strong efforts are being made to eliminate lead from materials which ultimately might end up in human beings. Recently considerable efforts have been made to remove or at least reduce the lead content from plumbing brasses that come in contact with potable water. U.S. Pat. No. 4,879,094 is an example.
In bearing and bushing bronzes lead is used primarily as a lubricating agent which also helps machinability. Currently there are many pump installations handling water that contain leaded bearings. Lead from them can possibly contaminate water being pumped. Furthermore, many machine shops buy lead containing bars and tube stocks to machine them into bushings and bearings. This might expose machinists to lead-bearing dusts if not fully protected. Additionally, lead-bearing scrap requires proper handling and recycling to prevent lead from entering the environment.
This establishes the need for a low friction bearing alloy which does not contain any highly toxic material like lead. In fact, there are already are some lead-free alloys with low friction. Examples are nickel-base alloys of Thomas and Williams (U.S. Pat. No. 2,743,176) and of Larson (U.S. Pat. No. 4,702,887) and copper-nickel alloy of Sahu (U.S. Pat. No. 5,242,657). However, these alloys are many times more expensive than common bearing alloys like C932 and C936.